1. Field of the Invention
The present disclosure relates to a method for fabricating display devices, more specifically, to a method of fabricating flexible electronic devices.
2. Description of the Related Art
A flexible display device can display information even though it is folded or bent, by means of forming display thereof unit on a flexible substrate. Therefore, the flexible display device is with a vast application prospect in field of portable electronic devices, wherein, the display equipments adopting the flexible display device comprise: Cholesteric Liquid Crystal Display (“LCD”, hereinafter), Electrophoresis Device and Organic Light-emitting Diode (“OLED”, hereinafter) and so on.
OLED mainly consists of a cathode layer where electrons can be injected, and an anode layer where holes can be injected. A voltage of suitable polarity is applied between the cathode layer and the anode layer to combine the holes and the electrons to release energy by lighting, i.e., electrofluorescence. Thus, OLED is Self-Illumination, and consequently, the back-lighting is unnecessary. Therefore, a light, thin and flexible display can be achieved by OLED. In the related art, the OLED is combined with a flexible substrate and a TFT backplane to fabricate a flexible OLED device, where the flexible substrate technology and de-bonding technology is pivotal.
The flexible substrates applied in the flexible display devices mainly include: organic plastic substrate, such as PC, PET, PEN, PES, PI, composite material substrate made from organic material and inorganic material by means of laminating or other methods and metal substrate containing stainless steal or aluminum.
Presently, the usage of the flexible substrate mainly includes the following two methods, i.e., the pre-prepared sheet material is provided, then it is bonded to a rigid substrate, such as glass, by binder; and the organic polymer precursor, such as polyimide precursor, is coated on the hard substrate.
The flexible substrate is required to be with the excellent properties of surface topography, thermo stability, low thermal expansion coefficient and reliability. Particularly, along with the popularity of the smart phone, the smart phone is of more and more function. The screen is the mainly interactive interface with user. The high resolution and large size panel are extremely important. And, the requirement for the flexible electronic device is higher and higher.
In the fabrication of the flexible electronic device, presently, inorganic powder is doped into an inorganic material precursor with a purpose to obtain a coefficient of thermal expansion (CTE) of 20 ppm/° C. (SID2010, Jia-Ming Liu and so on, Invited Paper: High Performance Organic-Inorganic Hybrid Plastic Substrate for Flexible Display and Electronics), and to control and improve dimensional and thermal stability thereof. However, it is still different from the coefficient of thermal expansion of the rigid substrate, for example, the coefficient of thermal expansion of glass is 3.39 ppm/° C. Therefore, when fabricating the flexible electronic device, interlaminar stress will generates, leading to a warp in the substrate, and subsequently leading to stripping or cracking of membrane. Finally, various display defects will incur.
Meanwhile, permeability of the flexible substrate to oxygen or moisture is also important. For example, the organic light-emitting diode is easily affected by the oxygen or the moisture because the permeation of the oxygen or the moisture reduces the function and life of the organic light-emitting diode.
The de-bonding technology means a such technology where after a required electronic device is fabricated from a flexible substrate attached to a rigid substrate, such as glass, the flexible substrate and the rigid substrate are separated.
However, in the above de-bonding process, the amorphous silicon is applied as sacrificial layer and laser equipment is applied. Consequently, the cost of the product is high.
FIG. 1 is a structure diagram for de-bonding layer disclosed by ITRI in related art. As shown in FIG. 1, ITRI disclosed a technology for de-bonding layer (SID2010, Cheng-Chung Lee and so on, Invited Paper: A Novel Approach to Make Flexible Active Matrix Displays): successively, Layer 12 is stuck on Rigid Glass Substrate 11, wherein, Layer 12 has a suitable bonding ability; next, a solution of PI precursor is coated with a coating area bigger that de-bonding layer area; next, the PI solidifies to form PI Membrane 13; next, normal TFT process is actualized on PI Membrane 13 to form Device, such as TFT 14; finally, PI Membrane 13 is cut along with edges of DBL layer, Layer 12. The bonding ability of PI Membrane 13 to Layer 12 is weak, consequently, Layer 12 can be easily separated from the PI membrane after the cutting process.
The above-mentioned de-bonding technology is simplified. However, PI Membrane directly contacts to Rigid Substrate 11 at outer parts thereof, the generated cohesive force will lead to an inaccurate alignment in TFT process.
Furthermore, in the above-mentioned process, a gas barrier layer (containing SiNx and composite layer) is formed on PI Membrane to solve the problem of permeability. The gas barrier layer, in part, overcomes the permeability of water/oxygen of PI Membrane 13. However, there is still a difference of coefficient of thermal expansion, leading to an inaccurate alignment in the following TFT process because of stress. Particularly, when the technology is carried out on a bigger size glass substrate, bigger than that of G2 generation, the problem will be more serious. Therefore, the yield rate of product is decreased.
U.S. Patent No. 2008309867A1 has disclosed a fabrication of a thin-film flexible electronic device of the screen type that includes a plurality of thin-film components on a glass support a starting support is prepared, including a rigid bulk substrate and a glass sheet fastened to the rigid bulk substrate by reversible direct bonding so as to obtain a removable interface. The plurality of thin-film components are fabricated on the glass sheet. The glass sheet is separated from the rigid bulk substrate by disassembling the interface and, the glass sheet and the plurality of thin-film components are transferred to a final support.
Korea Patent No. 20040111403A has disclosed an organic luminescence device and its production method. An organic luminescence device uses a substrate with a gas-barrier film in which a gas-barrier film containing an amorphous oxide and at least two kinds of oxides selected from the group consisting of boron oxide, phosphorus oxide, sodium oxide, potassium oxide, lead oxide, titanium oxide, magnesium oxide, and barium oxide is formed on a substrate. The selected two kinds of oxides are a combination of an oxide of an element having a large atomic radius and an oxide of an element having a small atomic radius. The substrate is made of glass or plastic. As a result, the organic luminescence device using a substrate excellent in gas-barrier capability to prevent the infiltration of oxygen, water vapor and so on from outside is provided. Consequently, it did not solve the problem of increasing the cost.